The present invention relates to an excavation roof support, and more particularly to an advancing excavation roof support.
There are already known various types of excavation roof supports which, generally speaking, include a base, at least one shield extending above the base, and various arrangements for supporting the shield on the base and for changing the position of the shield relative to the base. The present invention will be illustrated and described as embodied in a particular type of an excavation roof support, but it will be appreciated that its utilization in other types of roof supports is equally feasible. In this type of roof support, the base has a shielding portion at its end facing away from the excavation face, the shielding portion being rigidly connected to this end of the base and extending upwardly therefrom. A shield is pivotally connected to the shielding portion in its upper region, and a pit prop extends between the base and the shield and serves the purpose of pivoting the shield relative to the base so as to accommodate the roof support to various seam thicknesses. The shield has a free end spaced from the base, and a roof-supporting cap is pivoted to the free end of the shield. An advancing arrangement is mounted on the base, and extends between the latter and a conveyor which is located between the base and the excavation face. Experience with this conventional type of a roof support has shown that excellent results are obtained so long as the floor underneath the base is relatively rigid. On the other hand, it has been found that, when the excavation floor is relatively soft or cloddy, the end of the base which is subjected to the highest forces, that is the end of the base which is closest to the excavation face, has the tendency to dig into and penetrate the excavation floor to a certain extent so that, when the roof support advances toward the receding excavation face, the forward end of the base damages, rips, or otherwise destroys the excavation floor. This is, of course, disadvantageous not only from the point of view of quality of the excavation, but also for the reason that it is necessary to utilize a much higher force for advancing the roof support than would otherwise be necessary if the end of the base which is closest to the excavation face did not dig into the excavation floor.
This problem has already been recognized, and has been proposed to eleviate or eliminate this problem in various ways. So, for instance, inasmuch as the roof support is not used in isolation, but rather in combination with a plurality of identical roof supports which are arranged in a row along the excavation face and which advance one after the other, one of the conventional ways of dealing with this problem is to mount lifting mechanisms on the neighboring roof supports, the lifting mechanisms of each two roof supports being used for lifting the forward end of the roof support base located between them. In this manner, the base which has dug into the excavation floor is lifted to a certain extent upon which the roof support is advanced either immediately, or only after placing supporting beams or other bolstering elements underneath the base. It will be appreciated that this conventional arrangement requires a rather substantial capital investment and laborious manipultion. Also, less than satisfactory results are achieved with this arrangement at the ends of the row of supports.